As an example of the electric field radiation device applied to various devices such as the X-ray apparatus, the electron tube and the lighting system, there has been known a configuration in which voltage is applied between an emitter (an electron source formed of carbon etc.) and a target which are positioned (which are separated at a predetermined distance) while facing to each other in a vacuum chamber of a vacuum enclosure, an electron beam is emitted by field emission (by generation of electrons and emission of the electrons) of the emitter, and by colliding the emitted electron beam with the target, a desired function (for instance, in the case of the X-ray apparatus, a radioscopy resolution by external emission of X-ray) is obtained.
Further, suppression of dispersion of the electron beam emitted from the emitter, for instance, by employing a triode structure formed with a grid electrode interposed between the emitter and the target, and/or by shaping a surface of an electron generating portion (a portion that is positioned at an opposite side to the target and generates electrons) of the emitter into a curved surface, and/or by arranging a guard electrode, which is at the same potential as the emitter, at an outer circumferential side of the emitter, has been discussed (e.g. Patent Documents 1 and 2).
It is desirable that the electron beam be emitted by generating the electrons from only the electron generating portion of the emitter by the above application of voltage. However, if an undesired minute protrusion or dirt etc. exists in the vacuum chamber, an unintentional flashover pheanomenon easily occurs, and a withstand voltage performance cannot be obtained, then a desired function may not be able to be obtained.
This is, for instance, a case where a portion at which a local electric field concentration easily occurs (e.g. a minute protrusion formed during working process) is formed at the guard electrode etc. (the target, the grid electrode and the guard electrode, hereinafter simply called the guard electrode etc., as necessary), a case where the guard electrode etc. adsorb gas component (e.g. a residual gas component in the vacuum enclosure) and a case where an element causing the electron to be easily generated is contained in materials applied to the guard electrode etc. In these cases, the electron generating portion is formed also at the guard electrode etc., and a quantity of generation of the electron becomes unstable, then the electron beam easily disperses. For instance, in the case of the X-ray apparatus, there is a risk that X-ray will be out of focus.
Therefore, as a method of suppressing the flashover phenomenon (as a method of stabilizing the quantity of generation of the electron), for instance, a method of performing a voltage discharge conditioning process (regeneration (reforming); hereinafter simply called a regeneration process, as necessary) that applies voltage (high voltage) across the guard electrode etc. (e.g. between the guard electrode and the grid electrode) and repeats discharge, has been studied.